Viruses and Cancer The earliest relationship between cancer and viruses was demonstrated in early 1900s, when chicken leukemia and chicken sarcoma were transferred to healthy animals by cell-free filtrates.
The transformation of Normal Cells into Tumor Cells When activated, oncogenes transforms normal cells into cancerous cells. Viruses capable of producing tumors are called oncogenic viruses. Several DNA viruses and retroviruses are oncogenic. The genetic material of oncogenic viruses become integrated into the host cell’s DNA. Transformed cells lose contact inhibition, contain virus specific antigens (TSTA and T antigen), exhibit chromosome and abnormalities, and can produce tumors when injected into susceptible animals.
DNA Oncogenic Viruses Oncogenic viruses are found among: Adenoviridae Herpesviridae Poxviridae Papovaviridae
The EB virus, a herpes virus, causes Burkitt’s Lymphoma and nasopharyngeal carcinoma.
(Burkitt’s lymphoma) (Nasopharyngeal carcinoma)
RNA Oncogenic Viruses Among the RNA viruses, only retroviruses seem to be oncogenic. The virus’s ability to produce tumors is related to the production of reverse transcriptase. The DNA synthesized from the viral RNA becomes incorporated as a provirus into the host cell’s DNA. A provirus can remain latent, can produce viruses, or can transform the host cell.
Chickenpox (Varicellovirus) Chickenpox is one of the classic childhood diseases, and one of the most contagious. The affected child or adult may develop hundreds of itchy, fluid-filled blisters that burst and form crusts. Chickenpox is caused by a virus.
Latent Viral Infections A latent viral infection is one in which the virus remains in the host cell for long periods without producing an infection. Examples are cold sores and shingles.
Persistent Viral Infections Persistent viral infections are disease process that occur over a long period and are generally fatal. Persistent viral infections are caused by conventional viruses; viruses accumulate over a long period.